A few weeks after starting acetyl-L-carnitine, I became so sluggish I could hardly function. Could this be due to the supplement?

Answer:

Research has shown that carnitine can potentially impair the action of thyroid hormone -- which can cause fatigue and weakness. While this would not be expected to affect people with normal thyroid function, if you have low or borderline-low thyroid levels, this may explain your symptoms. Use of acetyl-L-carnitine or other forms of carnitine is not advisable when thyroid levels are low -- a condition particularly common among women older than 60 years.
This and several other potential side effects of acetyl-L-carnitine are described in the "Concerns and Cautions" section of ConsumerLab.com's Acetyl-L-Carnitine Supplements Review >>